1. Field of the Invention
The present invention relates to a toner for developing an electrostatic latent image for use in the development of an electrostatic latent image in an electrophotographic method or electrostatic recording method. More specifically, the present invention relates to a toner for use in an image-recording apparatus that can be utilized in a copying machine, printer or facsimile.
2. Description of the Related Art
In recent years, trends in technologies for printers have been directed toward the size reduction and speed-up of the machines. In addition, the printers have started to be used in various applications under various environments such as households and offices. In association with the above-mentioned diversification of the environments under which the printers are used, the printers have started to be used under a wide variety of environments ranging from an environment under which charging is hardly achieved as typified by a high-temperature and high-humidity environment to an environment under which excessive charging tends to occur as typified by a low-temperature and low-humidity environment.
It has been reported that the following problems generally occur under a high-temperature and high-humidity environment. That is, the so-called fogging in which faultily charged toner is printed even on a white portion of an image owing to faulty charging of toner, and the so-called faulty transfer in which the faultily charged toner is not sufficiently transferred occur. Particularly in the case where cardboard is used, heat tends to be absorbed by the paper surface, therefore, the quantity of heat to be applied to the toner for sufficiently fixing the toner on the cardboard has to be increased. In such case, the occurrence of the fogging causes the faultily charged toner to be additionally stretched, as a result, the problem of the fogging tends to be more remarkable than that in ordinary paper. In addition, when the toner is left to stand under the high-temperature and high-humidity environment, the charging of the toner tends to have difficulty in rising up owing to, for example, the moisture absorption of the toner or a charging member, as a result, a detrimental effect due to the faulty charging tends to be more likely to occur than in ordinary cases.
Meanwhile, with the advent of the diversification of the environments under which printers are used, the printers have started to be used even in cold climate areas each of which has a temperature as low as nearly 0° C. during nighttime hours and is under an extremely-low-temperature and low-humidity environment even during daytime hours. Under the extremely-low-temperature and low-humidity environment, excessive charging of toner particularly intends to occur, and problems such as faulty transfer due to an increase in electrostatic adhesive force of the toner and faulty regulation of the toner due to an increase in degree of electrostatic agglomeration tend to be more likely to occur than under a low-temperature, low-humidity environment where the toner has been conventionally used. In view of the foregoing, a toner capable of maintaining stable chargeability under any environment has been required.
It has been reported as one approach to improve chargeability that charging stability can be improved by melting and kneading a salt-like structured silicate as a charge control agent into toner (see, for example, Japanese Translation of PCT International Application Publication No. 2003-515795 and Japanese Patent Application Laid-Open No. 2007-241187). It has also been reported as another approach that a reduction in chargeability under a high-temperature and high-humidity environment can be suppressed by mixing a zeolite into a charge control resin having a sulfonic group as a substituent to cap the sulfonic group with the pores of the zeolite (see, for example, Japanese Patent Application Laid-Open No. 2005-070520). However, the zeolite used in the above-mentioned approaches has a large ratio of aluminum, and the water-absorbing property of the zeolite itself is high, therefore, it has been difficult to say that charge of the toner is sufficiently controlled under the high-temperature and high-humidity environment. Further, it is found that, in the above-mentioned approaches, the zeolite is present in the toner, and the addition of the zeolite exerts a small improving effect on triboelectric charging, and hence such a problem that sufficient charge rising performance cannot be obtained in printing after the toner has been left to stand for a while following printing on a large number of sheets particularly under the high-temperature and high-humidity environment arises.
It has also been reported that chargeability after printing on a large number of sheets can be improved by causing zeolite particles to adhere to toner particles in order to suppress the contamination of a member (see, for example, Japanese Patent Application Laid-Open No. 2002-244339). However, a zeolite used in the above-mentioned approach has a large ratio of aluminum, and the water-absorbing property of the zeolite itself is high, therefore, there has been a problem that charge rising performance cannot be obtained under a high-temperature and high-humidity environment.
As described above, no conventional toner can sufficiently provide satisfactory images under any use environment in high-speed, long-lifetime machines currently requested in the market. Accordingly, additional improvements have been demanded at present.